<template>
    <div class="Child">
      <h3>我是Child组件</h3>
      {{ sum }}
    </div>
  </template>
  
  <script >
  import {ref} from 'vue'
    export default {
      name: 'Child',
      setup(){
        let sum = ref(0)
        return {sum}
      }
    }
  </script>
  
  <style>
    .Child {
      background-color: skyblue;
      padding: 10px;
    }
  </style>